Hurricane Harvey: Death toll rises to 18 as 'catastrophic' storm now heaviest downpour in US history

A family is evacuated on an air mattress from the Hurricane Harvey floodwaters in Houston, Texas August 29, 2017. REUTERS/Rick WilkingWater from Addicks Reservoir flows into neighborhoods as floodwaters from Tropical Storm Harvey rise Tuesday, Aug. 29, 2017, in Houston. (AP Photo/David J. Phillip)U.S. President Donald Trump (C) llistens during a briefing on Tropical Storm Harvey relief efforts at the Texas Department of Public Safety Emergency Operations Center in Austin, Texas, U.S., August 29, 2017. REUTERS/Carlos BarriaU.S. President Donald Trump speaks during a tour of the Texas Department of Public Safety Emergency Operations Center in Austin, Texas, U.S., August 29, 2017. REUTERS/Carlos BarriaU.S. President Donald Trump and first lady Melania Trump arrive at Austin international airport in Austin, Texas, U.S., August 29, 2017. REUTERS/Carlos BarriaU.S. President Donald Trump and first lady Melania Trump arrive at Austin international airport in Austin, Texas, U.S., August 29, 2017. REUTERS/Carlos Barria

A curfew has been imposed in Houston where more than 13,000 people have been rescued after a catastrophic storm that is now the heaviest tropical downpour in US history.

With its flood defences strained, the crippled city anxiously watched dams and levees to see if they would hold until the rain stops.

FILE PHOTO: A woman uses a coat hanger to try and retrieve an item from a destroyed house after Hurricane Harvey struck Fulton, Texas, August 26, 2017. REUTERS/Rick Wilking/File PhotoWater from Addicks Reservoir flows into neighborhoods as floodwaters from Tropical Storm Harvey rise Tuesday, Aug. 29, 2017, in Houston. (AP Photo/David J. Phillip)U.S. President Donald Trump and first lady Melania Trump arrive at Austin international airport in Austin, Texas, U.S., August 29, 2017. REUTERS/Carlos BarriaDenise Vital, who evacuated her flooded home from Tropical Storm Harvey, watches over her 3-month-old godson at the Lake Charles Civic Center in Lake Charles, Louisiana, U.S., on August 29, 2017. Vital, who's home was destroyed by Hurricane Rita in 2005 said, "You have to keep pushing forward." REUTERS/Jonathan BachmanA car dealership is covered by Hurricane Harvey floodwaters near Houston, Texas August 29, 2017. REUTERS/Rick WilkingA truck carrying generators is stuck in Hurricane Harvey floodwaters near Alvin, Texas August 29, 2017. REUTERS/Rick WilkingA cow swims trying to get out of the Hurricane Harvey floodwaters near East Columbia, Texas August 29, 2017. REUTERS/Rick WilkingA family is evacuated on an air mattress from the Hurricane Harvey floodwaters in Houston, Texas August 29, 2017. REUTERS/Rick WilkingA woman talks to her rescuer after being evacuated by boat from the Hurricane Harvey floodwaters in Houston, Texas August 29, 2017. REUTERS/Rick WilkingA woman holds a carrier with her pet after being evacuated by boat from the Hurricane Harvey floodwaters in Houston, Texas August 29, 2017. REUTERS/Rick WilkingAn evacuee holding two dogs reacts after his rescue by Texas National Guardsmen from severe flooding due to Hurricane Harvey in Cypress Creek, Houston, U.S. August 28, 2017. U.S. Army National Guard/Capt. Martha Nigrelle/Handout via REUTERS. ATTENTION EDITORS - THIS IMAGE WAS PROVIDED BY A THIRD PARTYA man is evacuated by boat with his dog from the Hurricane Harvey floodwaters in Houston, Texas, U.S. August 29, 2017. REUTERS/Rick WilkingU.S. President Donald Trump and first lady Melania Trump arrive at Austin international airport in Austin, Texas, U.S., August 29, 2017. REUTERS/Carlos BarriaU.S. President Donald Trump and first lady Melania Trump arrive at Austin international airport in Austin, Texas, U.S., August 29, 2017. REUTERS/Carlos Barria

Meteorologists offered the first reason for hope, with a forecast of less than an inch of rain and even a chance of sunshine.

But the human toll continued to mount, both in deaths and in the ever-swelling number of scared people made homeless by Storm Harvey.

U.S. President Donald Trump and first lady Melania Trump arrive at Austin international airport in Austin, Texas, U.S., August 29, 2017. REUTERS/Carlos Barria

The city's largest shelter was overflowing when the mayor announced plans to create space for thousands of extra people by opening two and possibly three more mega-shelters.

"We are not turning anyone away. But it does mean we need to expand our capabilities and our capacity," Sylvester Turner said. "Relief is coming."

In an apparent response to scattered reports of looting, the mayor imposed a curfew, which he later amended to run from midnight to 5am, instead of beginning at 10pm.

He told a news conference that there is no reason for people to be on the streets during those hours.

Police Chief Art Acevedo said that curfew violators will be stopped, questioned, searched and arrested.

The rescues went on, and federal and local agencies said they had lifted more than 13,000 people out of the floodwaters in the Houston area and surrounding cities and counties.

U.S. President Donald Trump (C) llistens during a briefing on Tropical Storm Harvey relief efforts at the Texas Department of Public Safety Emergency Operations Center in Austin, Texas, U.S., August 29, 2017. REUTERS/Carlos Barria

Louisiana's governor offered to take in Harvey victims from Texas, and televangelist Joel Osteen opened his Houston megachurch, a 16,000-seat former arena, after critics blasted him on social media for not acting to help families displaced by the storm.

The death toll from Harvey rose to at least 18 as the Harris County, Texas, forensic office reported three more fatalities.

They include an 89-year-old woman, Agnes Stanley, who was found floating in floodwater in a home, and a 76-year-old woman who was found floating in floodwater near a vehicle. Her name was not released.

A 45-year-old man, Travis Lynn Callihan, left his vehicle and fell into floodwaters, and was taken to hospital, where he died on Monday.

Family members and authorities have reported at least 18 deaths, although the bodies of some victims apparently swept away in the floodwaters have not been found.